1. Field of the Invention
This invention relates to a condensation sensor which detects the existence of a condensate film of gas inside a sealed space where a gas for decontamination is supplied. The condensate film of gas is formed on the inside surface of the sealed space or on an object inside the space. The invention also relates to a method of controlling the condensate film inside the sealed space with the condensation sensor.
2. Description of the Prior Art
In manufacturing processes, such as for medical supplies and food, an operation in a sterilized condition is indispensable. Decontamination management inside a sealed space where a decontamination operation is performed needs to be carried out correctly and strictly. In the structure which supplies the gas for decontamination to the sealed space and decontaminates the inside of the sealed space, it has been known in recent years that there is a close relationship between the condensation phenomenon of the gas for decontamination inside the sealed space and the change of the number of residual bacilli on the surface of a decontamination subject inside the sealed space. Since it is very important to know when the supplied gas for decontamination begins to condense in the sealed space, a condensation sensor is provided for detecting when condensation starts.
FIG. 11 illustrates a condensation sensor (A) with a conventional structure, as disclosed in FIGS. 1–3 of International Publication No. PCT/WO01/71321, which is equipped with a light source (a) which emits light of predetermined wavelength, a glass window (b) of fixed thickness and a light sensor (c) which measures the amount of light emerging from the window (b). As shown in FIGS. 12a and 12b, the upper surface of the glass window (b) of the condensation sensor (A) faces inside a sealed space (D) where the gas for decontamination is supplied. On the other hand, the undersurface side of the glass window (b) is fixed to the surface of a wall of the sealed space (D) facing away from the sealed space (D). In this structure, a light from the light source (a) emerges into a right angled prism (FIG. 11) from the undersurface side of the glass window (b) as shown in FIG. 11. The light sensor (c) detects the light which penetrates the inside of the glass window (b) and measures the amount of light.
In this structure, if the gas saturates inside the sealed space after supplying the gas for decontamination inside the sealed space (D), a condensation phenomenon happens on the upper side of the glass window (b) facing the sealed space (D) and a condensation film is formed on the glass window (b). In this state, light emitted from the light source (a) repeatedly passes through the inside of the glass window (b) and reflects. Light irradiated out of the glass window (b) escapes and is scattered about in the plane of the condensation film bordering the glass window (b). For this reason, the intensity of a beam measured by the light sensor (c) decreases compared to when there is no condensation. By using such a phenomenon, a condensation start time of a condensation state of the gas for decontamination on the surface of the decontamination subject inside the sealed space (D) can be determined by changing the amount of light with the condensation sensor (A).
However, the structure of the decontamination subject is usually very complicated and not a plane like the glass window of the above-mentioned condensation sensor. Then, it is possible to have a portion on which the gas for decontamination cannot spread easily, i.e., a so-called cold spot. Therefore, there is a problem so that it cannot be presumed simply that a condensation state of the gas for decontamination on the glass window of the above-mentioned condensation sensor is in the condensation state on a surface of the decontamination subject. For this reason, even if a condensation sensor detects that condensation has occurred, the gas for decontamination in many cases is supplied superfluously or the decontamination subject may have an imperfect decontamination portion. Cost increases due to the increases in the decontamination time and aeration time, and there is also a possibility that the decontamination subject might corrode.
Since, in this composition, the light which passes through the glass window is scattered at the plane of the condensate film bordering the glass window, although this composition is detectable when the gas for decontamination condenses on the glass window surface, it is difficult to determine the mode of a subsequent condensate film correctly and in detail with respect to time. Also, since the upper surface of the glass window (b) needs to face the sealed space (D), as shown in FIGS. 12a and 12b, the installation is restricted because the condensation sensor (A) has to be disposed on the surface of a wall of the sealed space (D). Although a predetermined box (E) is proposed in which the condensation sensor (A) is fixed to the surface of a wall of the sealed space (D) detachably in order to secure convenience, it will be necessary to have a fan (c) and a larger size in order to circulate the air in box (E). Thus, the equipment is complicated. There are also problems in attracting disturbances, and exact detection is difficult to obtain.
Furthermore, since a light emerges inside a glass window of the conventional condensation sensor and the detected light repeatedly reflects inside the glass window, in order to acquire exact information, the length and thickness of the glass window must be determined to some extent (for example, a full length of the glass window is about 20 cm and the window thickness is about 1 cm). Therefore, there is a limit in miniaturizing the conventional condensation sensor.
Then, this invention provides a method for managing the condensate film in the sealed space using the condensation sensor which can determine the mode of a subsequent condensate film correctly and in detail with respect to time, and this condensation sensor can solve at least one of the above-mentioned problems while it can detect whether the gas used for decontamination condenses in the sealed space.